The truck has been running very rough lately. It misses and bucks while cruising around 2000rpms. If you floor the pedal, it goes away temporarily, but then comes back. It seems it happens more while cruising or accelerating lightly.

I have replaced the following things:

Coil, Fuel filter, CTS (coolant temperature sensor) in the past week, and the plugs/wires/cap are less than a year old.

Here is the strange part. If I disconnect the CTS, it runs perfect, but the check engine light is on. This is why I replaced the CTS, as I thought that was the problem, but it did not work. Since it runs fine with the Check Engine light on, it must be a sensor, maybe the Oxygen sensor??

my truck does the same thing i have been trying to trace it done for a while. what i found is that if i disconnect the green vac line from the egr valve and put elecrical tape over the green vac line to plug it it runs smooth no missing but i get the check engine light. i will try and disconnect the CTS and see what happens

My '92 (manual trans) did this for years. Took it to the dealer 4 times with no satisfaction. Then I posted to this board, and nitro94 had the solution:

- first, unplug the rubber hose from the EGR valve (mounted on the very back of the intake manifold). Plug the hose. The Check Engine light will come on, but ignore it.
- if this helps and eliminates the bucking, then you have to make a restrictor plate for the EGR valve. Instructions are on this board... do a search for restrictor plate.

The problem is that the EGR lets in so much exhaust gas (it stands for Exhaust Gas Recirculation) that the fuel mix is too lean and the cylinders don't fire with any power.

I made this EGR plate fix (didn't take me very long and was pretty easy), and since then (3 years now), the truck runs as smoothly as it did when brand new. Really solved the problem!

I tell ya, it has totally changed the truck. Runs smoothly and powerfully now. I actually think it runs better than when new. We use the truck to tow trailers (hay, grain, horses) and this fix has made a lot of difference.

Basically, the fix is to get a sheet of aluminum, cut out a piece to match the mounting plate of the EGR, drill a 1/8 inch hole into it where the EGR has an open hole, then sandwich it in between the EGR and its mounting on the intake manifold. Bolt it all back together.

That's the simple instruction... better instructions are posted here somewhere. Basically, you are just restricting the amount of exhaust gas going into the throttle body. And the truck still passes NJ's strict emissions every year with no problem.

how thick of aluminum did you get? I have been toying around with trying this myself. My truck just doesn't seem to run right. Bucks around 2000 rpm cruising. Feels like it's not getting enough gas. I have been reading a lot of posts that talk about this problem.

I wonder if it's the same problem I have. But it seems like it only bucks after coming off of a full or heavy throttle pull. It's been doing it since I bought the truck new in 91. Dealer couldn't figure it out 5 times. A friend bought the same truck at the same time and had the same problem. 4.9l w/ 5 speed man. trans. Sometimes it seems like it will rip the u-joints out of the thing. Wade

You can get a small sheet of aluminum at any home improvement store (Home Depot, Lowes, etc.), or your local hardware store. It doesn't have to be too thick, but shouldn't be so thin that it will burn. A lot thicker than aluminum foil, but not so thick that you can't bend the sheet.

Like azhound60 said, my '92 did this from about a month old. Four trips to the dealer. Finally, the dealer said "well we fixed it as much as we can"!!!

And it did it for years, especially after coming down off the throttle. I thought the rear end would rip apart, and in fact, after a few years, the rear axle seals started to leak and I had to replace them.

I tolerated it for about 4 years, then finally nitro94 on this board posted the restrictor plate solution. Now the truck runs smoother than my wife's Volvo wagon. When the I-6 runs right, it is smooth as silk.

Almost forgot. Before you do this fix, remove the battery's negative cable, and reattach it after you do the fix. Having no power will make the ignition/fuel mix computer forget its old settings, so when you start the truck, the computer will 'relearn' its settings with the new setup.

Originally posted by downdeephuskyjerk my truck does the same thing i have been trying to trace it done for a while. what i found is that if i disconnect the green vac line from the egr valve and put elecrical tape over the green vac line to plug it it runs smooth no missing but i get the check engine light. i will try and disconnect the CTS and see what happens

Do you leave the opening on the egr valve open or do you cover that too?

There's no need to cover the EGR valve's opening, because it is just using the vacumn from the hose to open its valve. So when there is no vacumn, the EGR valve doesn't open.

That's what you want to test... if the EGR isn't open and thus isn't pushing exhaust into the intake, does the engine run right?

You have to plug the little hose, however, so that it doesn't just suck a lot of extra air into the engine. I just plugged the hose with the cap from a bottle of transmission oil, and taped it in place. I guess you could just use duct tape or something similar instead.

Update, This morning I started my truck up and pulled the green line off the egr. There was vacum there. If I remember there should NOT be any vac. when cold. I plugged the green line and drove to work. (15 min) It seemed to run fine no stumbles or hesitations. First question: What is my next step? put a restrictor plate in or replace the egr valve. 2nd question: How long can I drive with that hose plugged? I don't have the funds to replace the egr right away. Can I drive like this for a couple of weeks?
As long as it runs alright I casn put up with CEL on. It also took about 10 min for the CEL to come on. ???

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